There are 25,000 kinds of fish. They live in water, but some, such as LUNGFISH, can live on land for short periods. Nearly all fish are covered with scales.
A typical fish has a streamlined body covered with a layer of silvery scales. There are a number of slender FINS on its body. The typical fish breathes by means of GILLS and swims by wriggling its tail from side to side. Many fish have an air-filled pouch in their bodies. It is called the swim-bladder and, by altering the amount of air in it, the fish can float easily at any depth it chooses.
Fish are cold-blooded animals. Most of them lay eggs, but some give birth to live young. A few even make nests for their eggs and young.
There are three main groups of fish. The FISH WITHOUT JAWS are sometimes not classed as fish. The SHARKS and their relatives have skeletons of soft cartilage instead of BONE. All other fish are
called 'bony fish'.

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